The present invention relates to a weft feeding device, particularly for shuttle-less looms, of the type comprising a fixed cylindrical drum on which a plurality of turns of thread is wound to constitute a feed reserve, means for advancing said reserve turns from the base towards the end of the drum and means for braking the outgoing thread which unwinds from the drum to be fed to the loom or to another textile machine with which the feeder is associable.
In this type of feeder it is very important that the braking means ensure a regular and constant tension of the outgoing thread, in order to avoid its breakage due to sudden variations in tension and to avoid the forming of socalled "baloons" or at least control their extent and keep it within acceptable limits.
Various types of braking means have been produced for this purpose, but all of them substantially belong to two categories: brush means and means with sheet metal or lamina arrays.
The first type comprises means which employ the braking action exerted by brushes which are supported by a ring and are pushed to contact the drum to a greater or smaller extent by adjusting the position of the ring with respect to the drum. This system is very effective for controlling "baloons", but scarcely effective for braking and therefore for controlling the thread's tension, due to the rapid wear of the bristles and to the discontinuity of the action exerted thereby. The second type of means, with arrays of metallic laminas, obviates this disadvantage but entail greater mechanical complexity due to the need to uniformly distribute among all the laminas of the array the pressure which pushes them into contact with the drum, in order that the elastic action exerted on the thread is equal for all the laminas.
For this purpose, it is known to arrange the array of laminas along a truncated-cone surface and to arrange said laminas in a cup-shaped support which is frontally arranged on the dome of the drum. The support can be elastic or rigid, and is adjustably pushed against the drum according to the braking pressure to be exerted. In the first case the elasticity of the support is relied upon to correctly and uniformly distribute the tension among the laminas, while in the second case the uniform distribution is achieved by suspending the support with a universal-type joint which gives said support the ability to self-center with respect to the drum.
The solution employing the elastic support is evidently scarcely reliable for the specified purpose, as it entails a rigorous structural uniformity of the elastic elements which constitute it.
The solution employing the self-centering support, on the other hand, entails a significant increase in the structural complexity of the feeder. Both solutions furthermore have the disadvantage that the points of tangency between the laminas and the drum are arranged on a circumference which is not the maximum circumference of the drum and that the radius of said circumference decreases significantly as the contact pressure rises; both circumstances considerably limit the locking action on the "baloon" of the thread and the range of adjustment of the braking action.